Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

178
FXUS63 KLOT 212312
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
612 PM CDT Thu May 21 2026

.KEY MESSAGES...

- Expect plenty of dry hours through Memorial Day Weekend.
  Isolated to widely scattered thunderstorms are possible late
  Saturday night into Sunday, potentially focusing primarily
  southeast of I-55 Sunday afternoon.

- Below average temperatures to close out the work week will
  trend to near to above average into next week, though notably
  cooler conditions will prevail near Lake Michigan.

&&

.DISCUSSION...
Issued at 240 PM CDT Thu May 21 2026

Through Saturday:

Seasonably strong surface high pressure centered over eastern
Canada will keep fairly status quo weather conditions, with
at times gusty northeast/east-northeast winds (strongest near
the lake) easing some tonight and then picking back up on
Friday. Extensive mid to high level cloud cover through Friday
will result in early Friday morning lows not quite as cool as
this morning (Thursday morning) but then only mid 60s to low 70s
highs inland Friday afternoon, perhaps approaching 60 lakeside.
Can`t rule out a few sprinkles out of the mid deck across
portions of far northern Illinois early to mid Friday morning as
a weak impulse passes by.

A fairly complex mid and upper level pattern will unfold Friday
afternoon into Saturday morning, with two main short-waves of
note. The first is a robust neutral to negatively tilted impulse
pivoting from the northern Plains to the central Canadian
Prairies. Our main short-wave of interest is a positively tilted
southern stream impulse (and weak surface low pressure reflection)
moving from the lower MS Valley to the central Great Lakes.

The existing dry sub-cloud layer air due to surface high
pressure influence may be tough to erode, especially with north
and northwestward extent, as stronger forcing will focus into
our southeast CWA and points east. There are also non-negligible
differences in the strength of the southern stream impulse, with
the ECMWF/EPS camp stronger and thus more aggressive in
spreading light rain/showers into a good chunk of the area.
Given the weaker forcing and drier posture of much of the non EC
guidance, kept PoPs in the 20-40% range (highest southeast of
I-55) and indicated sub mentionable (<15-20%) PoPs up in the
Rockford area. If and where rain does occur, a bulk of it would
likely occur in the overnight hours and thus less likely to
compromise outdoor plans.

In the wake of any lingering light rain/showers Saturday morning
over the eastern 1/3 to 1/2 or so of the CWA, expect dry
conditions the rest of the afternoon and early evening hours.
Temperatures will be a bit warmer, reaching primarily the low-
mid 70s away from Lake Michigan.

Saturday Night through Thursday:

Another modest short-wave impulse will move across the region
Saturday night into Sunday. Isolated to widely scattered showers
and maybe a few storms may drift eastward in tandem with the
wave into Sunday morning (~20-30% PoPs). Sunday afternoon, the
best chance for isolated to widely scattered renewed convective
initiation currently looks to focus primarily southeast of
I-55, closer to the departing short-wave. Even if/where any
thunderstorms develop, strong to severe storms are unlikely.
Temperatures will again step up some on Sunday away from the
lake, reaching the 75-80F range.

Summer-like warmth is forecast inland (highs in the lower to mid
80s) Memorial Day through midweek next week, while east to
southeast synoptic flow will be conducive to daily lake breezes
and cooler conditions lakeside. Some rain chances may return
midweek next week, though the progged pattern does not appear
supportive for organized convection, and there may be a play
for a bulk of the rain remaining south of our area.

Castro

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 612 PM CDT Thu May 21 2026

There are no key concerns for the 00Z TAF period.

NE winds at between 10 and 20 kt through mid-evening will ease
largely closer to 10 kt for the night, but with occasional gusts
as high as 20 kt. Expect NE winds between 10 and 20 kt during
the day on Friday.

A low potential for some spotty showers or sprinkles and
associated MVFR cigs exists Friday evening. Probabilities for
either are low enough through 06Z currently to omit a mention
in the 30-hr TAFs with MVFR becoming more likely during the
night.

Doom

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement through Saturday afternoon for ILZ006-
     ILZ103-ILZ104.

IN...Beach Hazards Statement until 4 AM CDT Friday for INZ001-
     INZ002.

LM...Small Craft Advisory until 10 AM CDT Saturday for the IL
     nearshore waters.

     Small Craft Advisory until 4 AM CDT Friday for the IN
     nearshore waters.

&&

$$

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